1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to multi-piece golf balls having a center, a mid layer and a cover.
2. Description of the Related Art
Golf players' greatest demand for golf balls is flight performance. Golf players emphasize flight performance with a driver, a long iron and a middle iron. The flight performance is correlated with the resilience performance of the golf ball. When the golf ball excellent in resilience performance is hit, the golf ball flies at a fast speed to accomplish great flight distance. The flight performance is also further correlated with spin rate. The golf ball flies at a small spin rate, thereby obtaining proper trajectory to accomplish great flight distance. In light of flight performance, golf balls which have high resilience performance and are not likely to be spun are desired.
Japanese Unexamined Patent Application Publication No. 2003-10359 (US2003/64828) discloses a golf ball having a center, a mid layer and a cover. This center has a small diameter and a small hardness. A spherical body including the center and the mid layer has an outer-hard/inner-soft structure. This structure accomplishes a small spin rate upon shots with a driver.
Japanese Unexamined Patent Application Publication No. 2003-19227 (US2003/109332) discloses a golfball having a center, an inner layer cover and an outer cover. In this center, a difference between a surface hardness and a central hardness is large. This center has an outer-hard/inner-soft structure. This structure accomplishes a small spin rate upon shots with a driver.
Japanese Unexamined Patent Application Publication No. 2003-205052 (US2003/166422) discloses a golfball having a center, a mid layer and a cover. This center has a small diameter and a small hardness. A spherical body including the center and the mid layer has an outer-hard/inner-soft structure. This structure accomplishes a small spin rate upon shots with a driver. A cover is made of polyurethane. This cover accomplishes a great spin rate upon shots with a short iron.
Japanese Unexamined Patent Application Publication No. 2003-325702 (US2003/211902) discloses a golfball having a center, a mid layer and a cover. This center contains a silicone rubber. A spherical body including the center and the mid layer has an outer-hard/inner-soft structure. This structure accomplishes a small spin rate upon shots with a driver.
Japanese Unexamined Patent Application Publication No. 2005-13455 (US2004/266557) discloses a golf ball having a core and a cover. In this core, a difference between a surface hardness and a central hardness is large. This core has an outer-hard/inner-soft structure. This structure accomplishes a small spin rate upon shots with a driver.
A core of a conventional golf ball uses a soft center and a hard mid layer in order to attain an outer-hard/inner-soft structure. The hardness distribution up to the central point of a center from the surface of a mid layer has a large level difference on the boundary of the center and the mid layer. This level difference deteriorates the suppression of spin. The flight performance of the conventional golf ball is insufficient.
Golf players' demand to the flight distance of the golf ball has been increasingly escalating. Golf player desires a golf ball which is not further likely to be spun. It is an object of the present invention to provide a golf ball excellent in flight performance.